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Fish tags create dinner bell effect, St Andrews University finds

Seal Image copyright St Andrews University
Image caption Scientists said the fish tags were creating a "dinner bell effect" for seals

Acoustic tags placed on fish to study their behaviour and movement are causing them to be easily hunted and eaten by seals, research has claimed.

St Andrews University scientists found grey seals were homing in on the pings from tags, which have been placed there to track the fish.

They said the fish tags were creating a "dinner bell effect" for predators.

The new findings have been published in Royal Society journal Proceedings of the Royal Society B.

Tests with captive grey seals showed they learned quickly to associate the sound made by the tags with the presence of an easy meal.

Ten juvenile seals who had not been exposed to acoustic tags before, were put to the test in a concrete pool with 20 boxes into which fish, tagged and untagged, were randomly placed for them to eat in 20 trials.

Finding prey

The research was carried out by Amanda Stansbury, Thomas Götz, Volker Deecke and Vincent Janik at St Andrews University's sea mammal research unit.

Ms Stansbury said: "The seals found the tagged fish sooner and with less searching than the fish without a tag.

"This means that the seals learned to use the sound from the pinging tags to find where their food was hidden.

"This tells us that seals can exploit new sounds, such as fish tags, and use them to their advantage."

The results show that scientists have to be careful when using acoustic tags to study fish.

Ms Stansbury said: "We expect that other marine mammals are similarly able to use such information to find prey.

"Tagged fish may be more detectable by predators, which could affect the results of fish studies.

"When we make noise in the sea, we need to consider how animals are affected.

"Our results show that such effects can be complicated. In our case they were beneficial to the seal but bad for the fish."

Previous studies had suggested the signal was audible to some predators, like seals, but this was the first research to find a "learned association between a signal and food leading to a 'dinner bell effect'," the authors said.

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